Psalms 13:5

In this I trust, that I shall receive forgiveness of my sin, in that I hope in your mercy through which you have worked salvation for all people.

His faith in God's mercy filled his heart with joy in his salvation; for joy and peace come by believing, Rom. xv. Believing, you rejoice, 1 Pet. i. Having put his trust in the mercy of God, he is fully assured of salvation, and that his heart, which was now daily grieving, should rejoice in that salvation.

But I have trusted in thy mercy,....

5 But I have trusted in thy mercy; my heart shall rejoice in thy salvation. 6 I will sing unto the L ORD , because he hath dealt bountifully with me. David, in affliction, is here pouring out his soul before God; his address is short, but the method is very observable, and of use for direction and encouragement.

What a change is here! Lo, the rain is over and gone, and the time of the singing of birds is come. The mercy-seat has so refreshed the poor weeper, that he clears his throat for a song. If we have mourned with him, let us now dance with him. David's heart was more often out of tune than his harp, He begins many of his psalms sighing, and ends them singing; and others he begins in joy and ends in sorrow; "so that one would think, " says Peter Moulin, "that those Psalms had been composed by two men of a contrary humour." It is worthy to be observed that the joy is all the greater because of the previous sorrow, as calm is all the more delightful in recollection of the preceding tempest. Sorrows remembered sweeten present joy." Here is his avowal of his confidence: "But I have trusted in thy mercy." For many a year it had been his wont to make the Lord his castle and tower of defence, and he smiles from behind the same bulwark still. He is sure of his faith, and his faith makes him sure; had he doubted the reality of his trust in God, he would have blocked up one of the windows through which the sun of heaven delights to shine. Faith is now in exercise, and consequently is readily discovered; there is never a doubt in our heart about the existence of faith while it is in action: when the hare or partridge is quiet we see it not, but let the same be in motion and we soon perceive it. All the powers of his enemies had not driven the psalmist from his stronghold. As the shipwrecked mariner clings to the mast, so did David cling to his faith; he neither could nor would give up his confidence in the Lord his God. O that we may profit by his example and hold by our faith as by our very life! Now hearken to the music which faith makes in his soul. The bells of the mind are all ringing, "My heart shall rejoice in thy salvation."

But I have trusted in thy mercy - Thou wilt not suffer me to fall; or if I have fallen, wilt thou not, for his sake who died for sinners, once more lift up the light of thy countenance upon me? Wilt thou not cover my sin? My heart shall rejoice in thy salvation - There is no true joy but of the heart; and the heart cannot rejoice till all guilt is taken away from the conscience.

But I have trusted in thy mercy - In thy favor; thy friendship; thy promises. His original confidence had been in God only, and not in himself. That confidence he still maintained; and now, as the result of that, he begins to exult in the confidence that he would be safe. The idea is, “I have trusted in the mercy of God; I still trust, and I will trust forever.” My heart shall rejoice in thy salvation - The word “salvation” here does not refer to salvation in the future world, but to deliverance from his present troubles, or to God’s interposition in putting him into a condition of safety. The idea is, that he had entire confidence that God would interpose, and that there would yet be cause to rejoice in that salvation as actually accomplished. He now calls on his heart to rejoice in the assurance that it would be his. So with us. There will not only be rejoicing in salvation when actually accomplished, but there may, and should be, in the firm conviction that it will be ours.